There are many scenarios in which it may be desirable to form a vacuum in a sealed enclosure. One such scenario involves the manufacture of vacuum insulated panels (“VIPs”). VIPs are a form of thermal insulation that provides an excellent level of thermal resistance (R-value) in a package that is very thin in comparison with the thickness of comparable conventional insulating materials (e.g., rolls and batts, loose-fill, rigid foam, and foam-in-place insulation). VIPs having a thickness of less than an inch can provide an R-value that would require several inches or even feet of traditional thermal insulation materials.
Because of these features, VIPs are attractive insulation alternatives in a wide range of applications where space and/or high thermal resistance is desired. Potential applications range from residential and commercial building construction, commercial and industrial furnace/refrigeration applications, medical storage and transport, residential appliances, etc. The high R-value, low thickness features of VIPs beneficially reduces the space considerations required for engineering these products and, for example, can lead to refrigerators with more storage, ovens with larger capacities, and medical supplies that can last longer in extreme field conditions.
VIPs include a gas-tight or nearly gas-tight enclosure, surrounding a rigid or semi-rigid core material, in which the air has been evacuated to form a vacuum. The VIP is typically constructed of overlying gas impermeable membrane panels that are sealed around their peripheries to define the enclosure. The core material is constructed of a highly porous material. The core material can have various material constructions and configurations. For example, the core material can be a panel of material (e.g., a sheet of glass fiber) positioned between the membranes or a bulk material (e.g., a loose fiber or foam) distributed evenly between the membranes. When the air is evacuated from the enclosure, the external pressure applied to the membranes compress the core which, in response, maintains some degree of spacing between the membranes. The porous core material provides the space between the membranes in which the vacuum is formed.
VIPs are costly in comparison to conventional forms of thermal insulation materials. One factor that lends to this cost differential is the high cost of manufacture of the VIPs. These manufacturing costs are driven not only by high material costs, but also by costly manufacturing equipment. The vacuum pumps traditionally used to evacuate air from the VIPs are costly pieces of equipment. Additionally, because the vacuum pumps require access to the VIP enclosure to draw the vacuum, maintaining and completing the seal between the membranes after the pump is removed requires additional equipment and cost.